CN101285976B - Transflective liquid crystal display device - Google Patents

Abstract

In order to increase the aperture ratio of the transflective liquid crystal display device and suppress light leakage. A transflective liquid crystal display device is provided, comprising: in a unit pixel, a reflective area including a reflector and a paired pixel electrode and a common electrode, and a transmissive area including a paired pixel electrode and a common electrode; provided to the a liquid crystal layer for the reflective area and the transmissive area; a storage capacitor for the reflective area and the transmissive area, provided on the bottom layer of the reflector, to change the potential of the pixel electrode by following the potential of the common electrode; and for Suppressing means for suppressing light leakage at the liquid crystal layer when the pixel electrode is influenced by the potential of the reflector due to capacitive coupling generated between the reflector and the pixel electrode.

Description

Transflective liquid crystal display device

Cross References to Related Applications

This application is based on, and claims the benefit of priority from, Japanese Patent Application No. 2007-106510 filed April 13, 2007, the disclosure of which is hereby incorporated by reference in its entirety.

technical field

The invention relates to a liquid crystal display device. More particularly, the present invention relates to a liquid crystal display device in which liquid crystals in a display area including a reflective area for realizing display by reflecting light incident from the outside are driven for display, and by transmitting light from a rear portion light to realize the transmissive area of the display.

Background technique

Liquid crystal display devices can be roughly classified into transmissive liquid crystal display devices and reflective liquid crystal display devices. Generally, a transmissive liquid crystal display device has a backlight source, and displays an image by controlling the amount of transmitted light from the backlight source. A reflective liquid crystal display device has a reflector for reflecting light from the outside, and displays an image by using the light reflected by the reflector as a display light source. A reflective liquid crystal display device does not require a backlight source, so it is superior to a transmissive liquid crystal display device in reducing power consumption, thickness, and weight of the device. However, since the reflective liquid crystal display device uses light in the environment as a display light source, the reflective liquid crystal display device has a disadvantage that contrast and visibility deteriorate under dark conditions.

Meanwhile, a transflective liquid crystal display device having advantages of both a transmissive liquid crystal display device and a reflective liquid crystal display device has been put into practical use as a display of a portable phone and a mobile terminal. A transflective liquid crystal display device has a transmissive area and a reflective area within a unit pixel. The transmissive area transmits light from the backlight source, and uses the backlight source as a display light source. The reflective area has a reflector, and uses external light reflected by the reflector as a display light source. With a transflective liquid crystal display device, power consumption can be reduced by turning off the backlight source under bright conditions and displaying images with reflective areas. In addition, when the surrounding environment becomes dark, by turning on the backlight light source and displaying images with transmissive areas, images can be displayed even in dark conditions.

Also, as a liquid crystal panel and a liquid crystal display device having a wide range of visible viewing angles, a lateral electric field mode such as an IPS mode (In-Plane Switching) generally called a wide viewing angle liquid crystal display panel has been put into practical use. With this IPS mode liquid crystal panel, liquid crystal molecules are uniaxially aligned by being parallel to a substrate, and voltage is applied in parallel to the substrate to rotate the liquid crystal molecules while maintaining an equilibrium state with the substrate. In other words, even when a voltage is applied, the liquid crystal molecules do not stand up with respect to the substrate, so theoretically a wide viewing angle can be obtained. In addition, the IPS mode liquid crystal display device has a pixel electrode and a common electrode formed on the same substrate, and a lateral electric field applied to the liquid crystal layer. With the IPS mode liquid crystal display device, for example, images are displayed by sufficiently rotating liquid crystal molecules in a direction parallel to the substrate, and a wider viewing angle than that of the TN mode liquid crystal display device can be obtained.

When the IPS mode is applied to an existing transflective liquid crystal display device, black display and white display are reversed. Therefore, under a normal drive system, the transmissive area is normally black and the reflective area is normally white.

17A and 17B show schematic cross-sectional views of unit pixels of a conventional transflective liquid crystal display device. As shown in FIGS. 17A and 17B , a unit pixel of a transflective liquid crystal display device includes a rear-side substrate 501 , an observer-side substrate 502 , and a liquid crystal layer 503 sandwiched between the two substrates. The unit pixel includes, within the pixel area, a reflective area 521 for reflecting light from the observer side, and a transmissive area 522 for transmitting light from the back side, and the liquid crystal layer 503 of the reflective area 521 and the transmissive area 522 is formed by Driven by a lateral electric field generated by a voltage applied parallel to the substrate face.

Furthermore, the back-side substrate 501 and the observer-side substrate 502 respectively include a first polarizing plate 520 and a second polarizing plate 523 on their outer sides. Also, two kinds of electrodes, that is, a pixel electrode 511 and a common electrode 512 are formed on the surface of the back side substrate 501 on the liquid crystal layer side. In a region portion where the pixel electrode 511 and the common electrode 512 are formed, a reflector 515 and an insulating layer 516 are provided between these electrodes and the back-side substrate 501 . Due to the existence of the insulating layer 516 , the thickness of the liquid crystal layer 503 in the reflective region 521 is half of the thickness of the liquid crystal layer 503 in the transmissive region 522 . Further, a backlight 504 functioning as a light source for transmissive display is provided on the outer side (lower side) of the polarizing plate (first polarizing plate) of the rear side substrate 501 .

Furthermore, as shown by the dotted lines in FIGS. 17A and 17B , the first polarizing plate 520 and the second polarizing plate 523 are arranged in such a manner that their polarization axes become orthogonal to each other. In the liquid crystal layer 503 , when no voltage is applied, the liquid crystal molecules are aligned to face along a direction deviated by 90 degrees from the polarization axis (light transmission axis) of the first polarizing plate 520 . For example, if the polarization axis of the first polarizer 520 is 0 degrees, the polarization axis of the second polarizer 523 is set to 90 degrees, and the main axis direction of the liquid crystal molecules of the liquid crystal layer 503 is set to 90 degrees. In the liquid crystal layer 503, the cell gap in the transmissive region 522 is adjusted so that the retardation Δnd (Δn is the anisotropy of the refractive index of the liquid crystal molecules, and d is the cell gap of the liquid crystal) becomes λ/2 (λ is the wavelength of light, for example, λ=550nm when green light is used as a reference), and the cell gap in the reflective region 521 is adjusted so that the retardation becomes λ/4.

Now, by referring to FIG. 17A , the optical action of the unit pixel of the above-structured transflective liquid crystal display device when no voltage is applied to the liquid crystal layer 503 will be described. First, linearly polarized light in a 90-degree direction (longitudinal direction) (hereinafter referred to as “90-degree linearly polarized light”) passing through the second polarizing plate 523 is incident on the liquid crystal layer 503 of the reflective region 521 . In the liquid crystal layer 503, the optical axis of the linearly polarized light incident on the liquid crystal layer 503 is in the same direction as the main optical axis of the liquid crystal molecules. Accordingly, incident light in a state of 90-degree linearly polarized light is transmitted through the liquid crystal layer 503 as it is, and it is reflected by the reflector 515 . In the case of linearly polarized light, it remains in the state of linearly polarized light even after being reflected. Thus, the reflected light in the 90-degree linearly polarized state is incident on the liquid crystal layer 503 again. Also, the 90-degree linearly polarized light is emitted from the liquid crystal layer 503 as it is, and is incident on the second polarizing plate 523 . The polarization axis of the second polarizer 523 is also 90 degrees, so the 90-degree linearly polarized light is transmitted through the second polarizer 523 . Therefore, when no voltage is applied, the reflective area 521 provides a white display.

Next, the transmissive region 522 to which no voltage is applied is described. Transverse linearly polarized light passing through the first polarizer 520 is incident on the liquid crystal layer 503 in the transmissive region 522 . In the liquid crystal layer 503 , the polarization direction of the incident light and the main optical axis direction of the molecules are orthogonal to each other, so the transversely linearly polarized light passes through the liquid crystal layer without changing the polarization state, and is incident on the second polarizer 523 . Since the polarization axis of the second polarizing plate 523 is 90 degrees, transmitted light cannot pass through the second polarizing plate 523, which results in providing a black display.

Next, by referring to FIG. 17B , when a voltage is applied to the liquid crystal layer 503, the optical action of the unit pixel of the transflective liquid crystal display device with the above-mentioned structure will be described. First, linearly polarized light in a 90-degree direction (longitudinal direction) passing through the second polarizing plate 523 is incident on the liquid crystal layer 503 of the reflective region 521 . By applying a voltage, the main axis direction of the liquid crystal in the liquid crystal layer 503 is changed from 0 degrees to 45 degrees with respect to the substrate plane. In the liquid crystal layer 503, the polarization direction of incident light and the main axis direction of the liquid crystal molecules are shifted by 45 degrees from each other, and the retardation of the liquid crystal is set to λ/4. Accordingly, longitudinal linearly polarized light incident on the liquid crystal layer 503 becomes clockwise circularly polarized light, and is incident on the reflector 515 . The clockwise circularly polarized light is reflected by the reflector 515 and becomes counterclockwise circularly polarized light. The counterclockwise circularly polarized light incident on the liquid crystal layer 503 passes through the liquid crystal layer 503 again, the circularly polarized light becomes transverse (0 degree) linearly polarized light and is incident on the second polarizing plate 523 . Since the polarization axis of the second polarizing plate 523 is 90 degrees, reflected light cannot pass through the reflector 515, which results in providing a black display.

Then, the transversely linearly polarized light passing through the first polarizer 520 is incident on the liquid crystal layer 503 in the transmissive region 522 . By applying a voltage, the direction of the main axis of the liquid crystal molecules in the liquid crystal layer 503 changes from 0 degrees to 45 degrees with respect to the substrate plane. In the liquid crystal layer 503, the polarization direction of incident light and the main axis direction of the liquid crystal molecules are shifted by 45 degrees from each other, and the retardation of the liquid crystal is set to λ/2. Therefore, the laterally linearly polarized light incident on the liquid crystal layer 503 becomes longitudinally linearly polarized light, and is incident on the second polarizing plate 523 . Thus, in the transmissive region 522, the second polarizer 523 enables the backlight passing through the first polarizer 520 to pass, which results in providing a white display.

According to the above-described transflective liquid crystal display device, in both cases of applying an electric field to the liquid crystal layer 503 and not applying an electric field to the liquid crystal layer 503, there is a case where white display and black display in the reflective region 521 and the transmissive region 522 are reversed. the inconvenience.

As a measure to solve this problem, uniformity of display in the reflective area and the transmissive area can be provided by applying voltages different from each other to the liquid crystal layers in the reflective area and the transmissive area of the transflective liquid crystal display device. For example, in the IPS transflective liquid crystal display device described above, the signal input to the common electrode of the reflection area (hereinafter referred to as reflection common signal) and the signal input to the common electrode of the transmission area (hereinafter referred to as transmission The common signal) is set in phases opposite to each other to apply voltages different from each other to the reflective area and the transmissive area.

Now, an example of the waveform of each input signal at the time of black display is shown in FIG. 18 . In the selection period of the scanning line, a potential difference is generated in the reflective region between the pixel electrode and the common electrode, and a voltage is applied to the liquid crystal layer (Vlc of FIG. 18A ), which results in providing black display. Simultaneously, a signal whose phase is opposite to that of the reflected common signal is input to the transmissive common electrode of the transmissive region. Therefore, in the selection period of the scanning line, no potential difference is generated between the pixel electrode and the common electrode, so no voltage is applied to the liquid crystal layer (Vlc of FIG. 18B ), which results in providing black display. Furthermore, in order to maintain the voltage applied to each liquid crystal layer during one frame period, it is necessary to change the potential of the pixel electrode by following the potential of the common electrode. Since the voltages held in the transmissive and reflective regions are different, it is necessary to provide a storage capacitor for each of the reflective and transmissive regions.

Now, the change in the potential of each electrode at the time of black display will be described. As shown in FIG. 19A, in the reflection area, it is necessary to apply a voltage to the liquid crystal layer at the time of black display. Therefore, a potential difference (assumed to be 5 V in this case) is generated between the common electrode and the pixel electrode in the selection period of the scanning line. Thereafter, the potentials of the pixel electrode and the reflector 1 become floating during the non-selection period of the scanning line. Therefore, by forming capacitance with the common electrode, the potential of the pixel electrode and the reflector 1 follows the reflected common signal by synchronizing with the reflected common signal. In addition, as shown in FIG. 19B, in the transmissive region, no voltage is applied to the liquid crystal layer at the time of black display. Therefore, the potentials of the common electrode and the pixel electrode become identical in the selection period of the scanning line. Thereafter, in the non-selection period of the scanning line, by forming capacitance with the common electrode, the potentials of the pixel electrode and the reflector follow the transmission common signal by synchronizing with the transmission common signal.

In addition, a unit pixel structure is also disclosed, with which the IPS transflective liquid crystal display is controlled by respectively providing storage capacitors to the reflection area and the transmission area of the liquid crystal layer to apply voltages different from each other to the corresponding areas The driving of the device enables the display of the reflective area and the transmissive area to be consistent (Japanese Unexamined Patent Application No. 2005-191061: Patent Document 1). In Patent Document 1, two TFTs (Thin Film Transistors) corresponding to each of the reflection area and the transmission area and first and second common electrodes corresponding to each of the reflection area and the transmission area are provided. The reflective area and the transmissive area of the liquid crystal layer are driven by inputting signals in opposite phases to each other to the two common electrodes.

In addition, a liquid crystal display device is also disclosed, wherein: a transistor and a storage capacitor are provided corresponding to each of the reflective region and the transmissive region; and the transistor Tr and the storage capacitor lines CsrL and CstL are provided to each of the reflective region and the transmissive region (Japanese Unexamined Patent Publication 2005-189570: Patent Document 2). In Patent Document 2, the storage capacitor in the reflective area is formed by the pixel electrode in the reflective area and the storage capacitor line CsrL, and the storage capacitor in the transmissive area is formed by the pixel electrode in the transmissive area and the storage capacitor line CstL. Therefore, storage capacitors are individually formed in each of the reflection area and the transmission area. With storage capacitors, different potentials can be applied to the pixel electrodes in the reflective and transmissive areas. In addition, the aperture ratio of the liquid crystal display device can be increased by forming the storage capacitance of the transmissive region in the bottom layer of the reflector of the reflective region.

However, with the liquid crystal display device of the transverse electric field type described above, it is impossible to obtain an excellent display by simply forming storage capacitors for the reflective area and the transmissive area in the bottom layer of the reflector. For example, when a reflective pixel electrode and a transmissive pixel electrode for forming a storage capacitor are provided in the bottom layer of the reflector in the structure of Patent Document 1, capacitive coupling exists between the reflector and the two pixel electrodes. Therefore, the potential of the pixel electrode is changed. Therefore, an offset voltage to be described later is applied to the liquid crystal layer, which causes deterioration of contrast due to light leakage. Similar problems also arise when the reflective storage capacitor forming portion and the transmissive storage capacitor forming portion overlap layers made of other conductive substances.

Contents of the invention

It is therefore a typical object of the present invention to provide a transflective liquid crystal display device capable of suppressing light leakage and providing high visibility.

In order to achieve the above-mentioned typical objects, a transflective liquid crystal display device according to a typical aspect of the present invention is a transflective liquid crystal display device comprising: in a unit pixel, a reflective region including a reflector and a pair of pixels an electrode and a common electrode; a transmissive region including a pair of pixel electrodes and a common electrode; and a liquid crystal layer provided to the reflective region and the transmissive region, and the transflective liquid crystal display device further includes provided in the bottom layer of the reflector, Storage capacitors for reflective and transmissive areas to change the potential of the pixel electrode by following the potential of the common electrode. The transflective liquid crystal display device further includes suppressing means for suppressing light leakage generated in the liquid crystal layer when the pixel electrode is influenced by the potential of the reflector due to capacitive coupling generated between the reflector and the pixel electrode.

Description of drawings

1 is a cross-sectional view illustrating a unit pixel structure of an exemplary embodiment of a transflective liquid crystal display device according to the present invention;

FIG. 2 is a plan view showing the structure of an exemplary embodiment of the transflective liquid crystal display device disclosed in FIG. 1;

FIG. 3 is a plan view showing the structure of an exemplary embodiment of the transflective liquid crystal display device disclosed in FIG. 1;

FIG. 4 is a plan view showing the structure of an exemplary embodiment of the transflective liquid crystal display device disclosed in FIG. 1;

FIG. 5 is a planar circuit structure diagram showing the configuration of an exemplary embodiment of the transflective liquid crystal display device disclosed in FIG. 1;

FIG. 6 shows a voltage waveform diagram of an exemplary embodiment of the transflective liquid crystal display device disclosed in FIG. 1;

7 is a graph showing the relationship between transmittance and applied voltage according to the exemplary embodiment of the transflective liquid crystal display device disclosed in FIG. 1;

FIG. 8 is a planar circuit configuration diagram showing the configuration of an exemplary embodiment of the transflective liquid crystal display device disclosed in FIG. 1;

FIG. 9 is a schematic planar circuit structure diagram showing the configuration of an exemplary embodiment of the transflective liquid crystal display device disclosed in FIG. 1;

10 is a cross-sectional view showing a unit pixel structure of another exemplary embodiment of a transflective liquid crystal display device according to the present invention;

FIG. 11 is a plan view showing the structure of an exemplary embodiment of the transflective liquid crystal display device disclosed in FIG. 10;

FIG. 12 is a plan view showing the structure of an exemplary embodiment of the transflective liquid crystal display device disclosed in FIG. 10;

FIG. 13 is a schematic planar circuit structure diagram showing the configuration of an exemplary embodiment of the transflective liquid crystal display device disclosed in FIG. 10;

14A-14C show an exemplary embodiment of the transflective liquid crystal display device disclosed in FIG. 10, wherein FIG. 14A is a graph showing the relationship between capacitance ratio and offset voltage, and FIG. 14B is a graph , showing the relationship between the transmittance and the applied voltage, and FIG. 14C is a graph showing the relationship between the thickness of the organic film and the offset voltage;

15 is a top view showing a unit pixel structure of another exemplary embodiment of a transflective liquid crystal display device according to the present invention;

16 is a top view showing a unit pixel structure of another exemplary embodiment of a transflective liquid crystal display device according to the present invention;

17A and 17B show an exemplary embodiment of an existing transflective liquid crystal display device, wherein FIG. 17A is a cross-sectional view showing a unit pixel structure when no voltage is applied between a pixel electrode and a common electrode, and FIG. 17B is a cross-sectional view showing a unit pixel structure when a voltage is applied between the pixel electrode and the common electrode;

FIG. 18 shows a voltage waveform diagram of an exemplary embodiment of the transflective liquid crystal display device disclosed in FIGS. 17A and 17B; and

FIG. 19 shows voltage waveform diagrams of the exemplary embodiment of the transflective liquid crystal display device disclosed in FIGS. 17A and 17B .

Detailed ways

Hereinafter, exemplary embodiments of the present invention will be described in detail by referring to the accompanying drawings.

The operating principle of the transflective liquid crystal display device will be described by referring to an example of the IPS transflective liquid crystal display device. As shown in FIGS. 17A and 17B , Δnd (retardation) of the liquid crystal layer 503 in the reflective region 521 is λ/4, and Δnd of the liquid crystal layer 503 in the transmissive region 522 is λ/2. The liquid crystal layer 503 is sandwiched between a polarizing plate 520 and a polarizing plate 523 whose transmission axes are orthogonal to each other. Therefore, the reflective region 521 becomes normally white, and the transmissive region 522 becomes normally black. In order for the reflective region 521 and the transmissive region 522 to have a uniform display, it is necessary to apply voltages different from each other to the liquid crystal layer 503 of the reflective region 521 and the liquid crystal layer 503 of the transmissive region 522 . Different voltages can be obtained by setting the phase of the signal (reflected common signal) input to the common electrode 512 of the reflective region 521 to be opposite to that of the signal input to the common electrode 512 of the transmissive region 522 (transmitted common signal).

18A and 18B illustrate the waveform of each input signal at the time of black display. In the selection period of the scanning line, a potential difference is generated between the reflective pixel electrode 511 and the reflective common electrode 512 in the reflective region 521, and a voltage is applied to the liquid crystal layer 503 of the reflective region 521 (Vlc of FIG. 18A). In this way, the display in the reflective area 521 becomes black. Simultaneously, a signal having a phase opposite to that of the signal for the reflective common electrode 512 is input to the transmissive common electrode 512 in the transmissive region 522 . Therefore, in the selection period of the scanning line, no potential difference is generated between the transmissive pixel electrode 511 and the transmissive common electrode 512, and thus no voltage is applied to the liquid crystal layer 503 of the transmissive region 522 (Vlc of FIG. 18B ). Therefore, the display in the transmissive area 522 becomes black.

In order to maintain the voltage applied to each liquid crystal layer 503 of the reflective area 521 and the transmissive area 522 during one frame period, it is necessary to change the potential of the pixel electrode 511 by following the potential of the common electrode 512 . Since the voltages held in the transmissive area 522 and the reflective area 521 are different, it is necessary to provide a storage capacitor for each of the reflective area 521 and the transmissive area 522 . Therefore, it is necessary to provide a transistor and a storage capacitor to each of the reflective area and the transmissive area of the unit pixel to realize the operation of the IPS transflective liquid crystal display device as described above.

As shown in FIG. 1 , FIG. 10 , FIG. 15 and FIG. 16 , exemplary embodiments of the present invention include storage capacitors Cst1 and Cst2 for tracking the potentials of the common electrodes 47 and 48 of the reflective region 21 and the transmissive region 22 The potentials of the reflective region 21 and the transmissive region 22 are changed. These storage capacitors Cst1 and Cst2 are arranged in the underlying layer of the reflectors 23 , 24 and 25 of the reflective region 21 . The storage capacitor Cst1 of the reflective area 21 is formed between the static electrode (reflective pixel electrode) 35 and the common electrode (reflective common electrode) 37 of the reflective area 21, and the capacitor Cal1 is formed between the reflectors 23, 23, 25 and the static electrode of the reflective area 21. between electrodes (reflective pixel electrodes) 35 . The storage capacitor Cst2 of the transmissive region 22 is formed between the static electrode (transmissive pixel electrode) 36 and the common electrode (transmissive common electrode) 38 of the reflective region 21, and the capacitor Cal2 is formed between the reflectors 23, 24, 25 and the static electrode of the reflective region 21. between electrodes (transmissive pixel electrodes) 36 . FIG. 5 shows an equivalent circuit according to an exemplary embodiment of the present invention.

That is, as shown in FIG. 5, the gate of the transistor TFT formed in the reflective region 21 is connected to the scan line 31, its source or drain is connected to the data line 32, and the other pole (source or drain) It is connected to the reflective pixel electrode A35 formed in the reflective region 21. Similarly, the gate of the transistor TFT formed in the transmissive region 22 is connected to the scan line 31, its source or drain is connected to the data line 32, and the other pole (source or drain) is connected to the TFT formed in the reflective region. 21 on the transmissive pixel electrode A36.

The reflector 23, 24 (25) is formed as a single continuous plate, and the capacitors Cal1 and Cal2 are arranged in the bottom layer of the reflector 23, 24 (25). Therefore, the reflective pixel electrode 35 and the transmissive pixel electrode 36 are capacitively coupled through the capacitors Cal1 and Cal2.

Now, problems occurring when the reflective pixel electrode 35 and the transmissive pixel electrode 36 are capacitively coupled through the capacitances Cal1 and Cal2 will be described. To describe the problem, the change in the potential of each electrode at the time of black display will be described in detail with reference to FIG. 19 and FIG. 6 . In the following description, it is assumed that the reflectors 23 and 24 are single reflectors in the form of a continuous integral body.

As shown in FIG. 19A , it is necessary to apply a voltage to the liquid crystal layer 16 in the reflective region 21 for black display. Thus, in the selection period of the scanning line 31, a potential difference (assumed to be 5 V in this case) is generated between the common electrode 47 and the pixel electrode 45. Thereafter, the potentials of the pixel electrode 45 and the reflectors 23 , 24 become floating during the non-selection period of the scanning line 31 . Therefore, through the storage capacitor Cst1 between the pixel electrode 35 and the common electrode 37, the potentials of the pixel electrode 35 and the reflectors 23, 24 will follow the reflected common signal by synchronizing with the reflected common signal.

As shown in FIG. 19B, in the transmissive region 22, no voltage is applied to the liquid crystal layer 16 at the time of black display. Thus, in the non-selection period of the scanning line 31, the potentials of the common electrode 48 and the pixel electrode 46 become identical. Thereafter, in the non-selection period of the scanning line 31, through the storage capacitor Cst2 between the pixel electrode 36 and the common electrode 38, the potentials of the pixel electrode 36 and the reflectors 23, 24 will follow the transmission common signal by synchronizing with the transmission common signal . However, when the reflector 23 and the reflector 24 are connected, the potential of the reflector 23 and the potential of the reflector 24 shown in FIGS. 19A and 19B are added. Therefore, as shown in FIG. 6A, it can be considered that the potential is fixed (in this case at 5V). As shown in FIG. 6B, under such conditions, in the transmissive region 22, when the potential of the common electrode 48 becomes 0 V, the potential of the pixel electrode 46 is affected by the reflectors 23, 24 due to capacitive coupling (capacitance Cst2). . Therefore, the potential of the pixel electrode 46 becomes larger than 0V. The capacitor Cal2 and the storage capacitor Cst2 are considered to be in series, so the potential difference between the reflectors 23, 24 and the common electrode 38 is distributed in the inverse ratio of the storage capacitor Cst2 to the capacitor Cal2. Therefore, if the potential difference between the reflectors 23, 24 and the common electrode 38 is V, the value of the storage capacitor Cst2 is Cst, the value of the capacitor Cal2 formed by the reflectors 23, 24 and the pixel electrode 36 is Cal, and the pixel electrode 48 The potential change ΔV of can be expressed by the following equation.

ΔV＝V×Cal/(Cst+Cal)

"ΔV" is called an offset voltage. A voltage of “ΔV” is applied to the liquid crystal layer 16 in the transmissive region 22 at the time of black display.

FIG. 7 shows an example of characteristics showing the relationship between transmittance and applied voltage. As can be seen from FIG. 7, when a voltage of 0.5 V or more is applied to the liquid crystal layer 16, the transmittance starts to increase. This voltage is called the threshold voltage. When the offset voltage ΔV is greater than the threshold voltage, the alignment of the liquid crystal is changed and light leakage occurs at the time of black display. Therefore, the contrast deteriorates. Similarly, due to the offset voltage ΔV, a sufficient voltage cannot be applied to the reflective region 21 , so light leakage also occurs there.

Therefore, in order to suppress deterioration of visibility caused by such light leakage, exemplary embodiments of the present invention further include suppressing means for suppressing Capacitive coupling between the capacitors Cal1 and Cal2 causes the pixel electrodes 35 and 36 to be affected by the potentials of the reflectors 23 , 24 and 25 to cause light leakage in the liquid crystal layer 16 .

As described above, the transflective liquid crystal display device according to the exemplary embodiment of the present invention is directed to a transflective liquid crystal display device including: within a unit pixel, the reflective region 21 including the reflector and the paired pixel electrodes 45 and a common electrode 47 , the transmissive region 22 including a pair of pixel electrodes 46 and a common electrode 48 ; and the liquid crystal layer 16 provided in the reflective region 21 and the transmissive region 22 . In addition, as shown in FIG. 1, FIG. 10, FIG. 15 and FIG. 16, as a basic structure, the transflective liquid crystal display device includes memory for the reflective area 21 and the transmissive area 22 provided in the bottom layer of the reflector 23, 24, 25. Capacitors Cst1 and Cst2, the storage capacitors Cst1 and Cst2 are used to change the potential of the pixel electrodes 45 and 46 to follow the potential of the common electrodes 47 and 48 . In addition, the transflective liquid crystal display device includes suppressing means for suppressing the pixel electrodes 35, 36 from being reflected due to the capacitive coupling of the capacitors Cal1 and Cal2 formed between the reflectors 23, 24, 25 and the pixel electrodes 35, 36. Light leakage occurs in the liquid crystal layer 16 due to the influence of the potentials of the devices 23, 24, and 25. Details of this suppression means will be described later.

In an exemplary embodiment of the present invention, due to the storage capacitors Cst1, Cst2 in the bottom layers of the reflectors 23, 24, 25 for the reflective area 21 and the transmissive area 22, the potential of the pixel electrode follows the potential of the common electrode by And change. Therefore, the voltage applied to the liquid crystal layer 16 of the reflective area 21 and the transmissive area 22 can be maintained in a certain manner during one frame period.

Due to the capacitive coupling caused between the reflectors 23, 24, 25 and the pixel electrodes 35, 36 because of the capacitances Cal1, Cal2, since the pixel electrodes 35, 36 are affected by the potentials of the reflectors 23, 24, 25, the liquid crystal layer 16 light leakage occurs. However, in an exemplary embodiment of the present invention, light leakage in the liquid crystal layer 16 can be suppressed by suppressing means.

As typical advantages according to the present invention, exemplary embodiments of the present invention include: providing storage capacitors for the reflective area and the transmissive area in the bottom layer of the reflector to change the potential of the pixel electrode by following the potential of the common electrode; Suppressing means for suppressing light leakage generated in the liquid crystal layer because the potential of the pixel electrode is affected by the potential of the reflector due to capacitive coupling generated between the reflector and the pixel electrode. Therefore, it becomes possible for the potential of the pixel electrode to follow the potential of the common electrode. Also, it is possible to suppress light leakage occurring in the liquid crystal layer due to capacitive coupling through the storage capacitor, and thus the visibility of the liquid crystal display device can be improved.

Next, specific examples of the transflective liquid crystal display device according to the present invention, especially the suppression means, will be described in more detail with reference to the accompanying drawings.

first exemplary embodiment

The suppressing means according to the first exemplary embodiment of the present invention is formed to suppress the offset voltage ΔV to be applied to the liquid crystal layer 16 by adopting a structure in which the capacitance Cal1 of the reflective region 21 and the capacitance Cal1 of the transmissive region The capacitor Cal2 of 22 is electrically isolated. Hereinafter, the first exemplary embodiment will be described in a concrete manner.

As shown in FIG. 1 , the unit pixel structure 10 of the liquid crystal display device according to the first exemplary embodiment includes a rear side substrate 18 configured with a reflective region 21 and a transmissive region 22, and a reflective common electrode A37 and a transmissive common electrode A38 are formed on the The reflective region 21 side of the observer-side surface of the back-side substrate 18 . In addition, the scan line 31 ( FIG. 2 ) is formed on the same plane as the plane on which the reflective common electrode A37 and the transmissive common electrode A38 are formed. As shown in FIG. 2, the transmissive common electrode A38, the scan line 31 and the reflective common electrode A37 are formed in parallel in the order of the transmissive common electrode A38, the scan line 31 and the reflective common electrode A37 toward the direction away from the transmissive region side. Also, as shown in FIG. 1 , the insulating layer 12 is formed on the viewer side of the back side substrate 18 by covering the transmissive common electrode 38 and the reflective common electrode A37 .

Also, as shown in FIG. 1 , the reflective pixel electrode A35 is formed to overlap the reflective common electrode A37 on the observer side of the reflective region 21 of the insulating layer 12 . In other words, the reflective pixel electrode A35 is formed above the reflective common electrode A37 when viewed from the observer side. Accordingly, the reflective storage capacitor Cst1 is formed on the back side (inside the insulating layer 12 ) of the reflective pixel electrode A35 together with the reflective common electrode A37 . Similarly, the transmissive pixel electrode A36 is formed to overlap the transmissive common electrode A38 on the observer side of the reflective region 21 of the insulating layer 12 . Accordingly, the transmissive storage capacitor Cst2 is formed on the rear side (inside the insulating layer 12 ) of the transmissive pixel electrode A36 together with the transmissive common electrode A38 .

Also, as shown in FIG. 2, a data line 32 to which a data signal is supplied for each pixel is formed so as to perpendicularly cross the transmissive common electrode A38, the scan line 31 and the reflective common electrode A37, the data line 32 is formed On the same plane as the plane on which the reflective pixel electrode A35 and the transmissive pixel electrode A36 are formed. As shown in FIG. 2, a switching device (hereinafter referred to as a switching device) for interconnecting each data line 32, the reflective pixel electrode A35, and the protruding portion (the portion encircled by a dotted line) of the transmissive pixel electrode A36 is formed. TFT). Moreover, as shown in FIG. 1, an insulating layer 13 is formed in the reflective region 21 and the transmissive region 22 by covering the viewer side of the insulating layer 12, which includes the reflective pixel electrode A35 and the transmissive pixel electrode A36 together with the insulating layer. .

Also, the organic thin film layer 14 is formed in the reflective region 21 on the observer side of the insulating layer 13 . The organic thin film layer 14 has an uneven pattern suitable for a reflector to be described later on the viewer side. Also, as shown in FIGS. 1 and 3 , the reflector 23 is formed on the viewer side of the organic thin film layer 14 so as to overlap the reflective pixel electrode A35 . That is, the reflector 23 is disposed over the reflective pixel electrode A35 when viewed from the observer side. With such a structure, a capacitor Cal1 is formed between the back side of the reflector 23 and the reflective pixel electrode A35. In addition, a reflector 24 is formed on the viewer side of the organic thin film layer 14 to overlap the transmissive pixel electrode A36. That is, the reflector 24 is disposed over the transmissive pixel electrode A36 when viewed from the observer side. With such a structure, a capacitance Cal2 is formed between the back side of the reflector 24 and the transmissive pixel electrode A36.

In addition, as shown in FIG. 3 , the reflector 23 and the reflector 24 are physically separated, so the capacitor Cal1 and the capacitor Cal2 described above are electrically isolated. The reflectors 23 and 24 are formed to have uneven patterns on their cross-sections to increase the scattering effect.

Furthermore, as shown in FIG. 1 , the leveling film layer 15 is formed by covering the observer side of the reflectors 23 , 24 of the reflective region 21 and the observer side of the insulating layer 13 of the transmissive region 22 with a leveling film. By adjusting the thickness of the leveling film layer 15, the cell gap of each liquid crystal layer in the reflective region 21 and the transmissive region 22 can be adjusted.

Before forming the reflective common electrode B47, the reflective pixel electrode B45, the transmissive common electrode B48, and the transmissive pixel electrode B46, contact holes a-d are formed in the reflective region 21 and the transmissive region 22, as shown in FIGS. 3 and 4 . Therefore, the reflective common electrode B47, the reflective pixel electrode B45, the transmissive common electrode B48, and the transmissive pixel electrode B46 are connected to the reflective common electrode A37, the reflective pixel electrode A35, the transmissive common electrode A38, and the transmissive pixel electrode through the contact holes a-d, respectively. A36.

And, as shown in FIG. 4 , the comb-shaped reflective common electrode B47 and the comb-shaped reflective pixel electrode B45 are arranged on the viewer side of the flat film layer 15 in such a way that the protruding parts of each electrode face the inner side of the opposite reflective region facing in the direction of . Therefore, in the reflective area 21, the reflective pixel electrodes B45 and the reflective common electrodes B47 are arranged in an alternating manner in a direction orthogonal to the longitudinal direction of the comb teeth. Similarly, the comb-shaped transmissive common electrode B48 and the comb-shaped transmissive pixel electrode B46 are arranged on the viewer side of the flattened film layer 15 of the transmissive region 22 in such a manner that the protruding portions of the electrodes are directed towards the reflective region. The direction of the inner side faces so as to be opposite. Therefore, in the transmissive region 22, the transmissive pixel electrodes B46 and the transmissive common electrodes B48 are arranged in an alternating manner in a direction orthogonal to the longitudinal direction of the comb teeth.

Moreover, as shown in FIG. 1, by covering the reflective pixel electrode B45, the reflective common electrode B47, the transmissive pixel electrode B46, and the transmissive common electrode B48, the liquid crystal layer 16 is formed on the upper layer (observer side) of the leveling film layer 15. Regarding the liquid crystal layer 16 , its retardation Δnd in the reflective region 21 is set to λ/4, and its retardation Δnd in the transmissive region 22 is set to λ/2. Also, an observer-side substrate 19 is provided on the observer side of the liquid crystal layer 16 . Thus, the unit pixels of the liquid crystal display device according to the present exemplary embodiment are configured.

The liquid crystal display device of this exemplary embodiment is constituted as described above, so the reflective common electrode B47, the reflective pixel electrode B45, the transmissive common electrode B48 and the transmissive An electric field is generated between the pixel electrodes B46 to rotationally drive the liquid crystal.

Now, the case where the reflectors 23 and 24 in the unit pixel structure of the liquid crystal display device 10 shown in FIGS. 1 to 4 are not electrically isolated is described. Figure 5 shows the equivalent circuit for this case.

As shown in FIG. 5, storage capacitors Cst1 and Cst2 corresponding to reflective and transmissive regions are respectively formed on the bottom layer side of the reflector. In this case, the reflective pixel electrode A35 and the transmissive pixel electrode A36 are also arranged opposite to the reflector with the insulating layer 13 and the organic thin film layer 14 interposed therebetween. Capacitive coupling of Cal and Cal2 therefore occurs between the respective pixel electrode and the reflector.

Because of this, the potentials of the reflective pixel electrode A35 and the transmissive pixel electrode A36 are affected by the potential of the reflector. Therefore, as shown in FIG. 6A, the potential of the reflective pixel electrode A35 (reflective pixel signal potential) and the potential of the reflective common electrode A37 (reflective common signal potential) in the reflective region 21 become smaller than that of the absence of the influence of the potential from the reflector. situation (Figure 19A). That is, it becomes less than about twice the value of the reflected common signal potential (arrow marked with *1)

In other words, when the reflectors 23 and 24 are not electrically isolated, the reflector potentials 1 and 2 shown in FIGS. 19A and 19B are summed. In this way, as shown in FIG. 6A, the potential can be considered to be fixed (in this case at 5V, the reflector potential). In this case, in the reflection area 21, when the reflection common signal potential becomes 5V, the potential of the reflection pixel electrode is lower than 10V in the non-selection period of the scanning line signal potential (arrow marked with *1). This means that it is not possible to apply sufficient voltage to the liquid crystal, which can cause light leakage.

Further, as shown in FIG. 6B , a potential difference is generated between the potential of the transmissive pixel electrode A36 (transmissive pixel electrode potential) and the potential of the reflective common electrode A38 (transmissive common signal potential) in the transmissive region 22 . This potential difference is larger than when there is no influence of the potential from the reflector (FIG. 19B: potential difference=0) (arrow marked with *2).

In other words, as shown in FIG. 6B, when the transmission common signal potential becomes 0V, the transmission pixel electrode potential is larger than 0V in the non-selection period of the scanning line signal potential (arrow marked with *2). In this case, it can also be considered that there is light leakage in the display because the voltage is not sufficiently blocked.

Here, it can be considered that the storage capacitance ( Cst1 , Cst2 ) and the capacitance formed by the reflective pixel electrode A35 , the transmissive pixel electrode A36 and the reflector are connected in series. Therefore, the reflector and the potential difference between the reflective common electrode A37 and the transmissive common electrode A38 are divided in inverse proportion to each capacitance. Therefore, assuming that the potential difference between the reflector and each common electrode is V, the value of the storage capacitor is Cst, and the value of the capacitance formed between the reflector and the pixel electrode is Cal, the change in potential of the pixel electrode by ΔV (in the following Herein referred to as "offset voltage") can be represented by the following equation.

ΔV＝V×Cal/(Cst+Cal)

Therefore, at the time of black display, an offset voltage (ΔV) is applied to the liquid crystal layer in the transmissive region. In this way, the voltage cannot be sufficiently blocked, thus causing light leakage.

FIG. 7 shows an example of the relationship between transmittance and applied voltage. As shown in FIG. 7, it is considered that the transmittance starts to increase when a voltage of 0.5 V or more is applied to the liquid crystal layer. This value (0.5V in this case) is called the threshold voltage. Therefore, when black is displayed in the transmissive region 22, when the offset voltage is larger than the threshold voltage, there is a change in the alignment of the liquid crystal, which causes light leakage. Similarly, since a sufficient voltage cannot be applied to the liquid crystal layer due to the influence of the offset voltage, light leakage also occurs in the reflective area 21 .

As a measure to solve this problem, in the structure of the unit pixel of the exemplary embodiment as described above, storage capacitors respectively corresponding to the reflective region 21 and the transmissive region 22 are formed on the back side of the reflector of the reflective region 21 (underlayer side), and the reflector is electrically isolated along the boundary line between the reflective storage capacitor forming part and the transmissive storage capacitor forming part. This makes it possible to suppress generation of an offset voltage, and thus light leakage in display of a pixel can be suppressed.

FIG. 8 shows an equivalent circuit on a TFT substrate within a unit pixel of the liquid crystal display device 10 shown in FIGS. 1 to 4 . As shown in FIG. 8 , scan lines 31 used to control TFTs (thin film transistors) as switching devices as control lines, and data lines 32 used to provide pixel electrode voltages to reflective and transmissive pixel electrodes through TFTs are orthogonal to each other. formed.

Here, TFTs 60 and 61 are formed by corresponding reflective regions 21 and transmissive regions 22. The gate of each TFT 60 and 61 is connected to the scan line 31, and the source or drain thereof is connected to the data line 32. In addition, the other electrode (source or drain thereof) of each TFT 60 and 61 is connected to the reflective pixel electrode A35 and the transmissive pixel electrode A36. As switching devices, other switching devices than TFTs, such as MIMs, can also be used.

As shown in FIG. 8, capacitive couplings C11, C12, and C13 (referred to as small capacitors) are respectively generated between the reflector 23 and the reflective common electrode B47, between the reflector 24 and the reflective pixel electrode B45, and between the reflector 23 , 24 and reflective common electrode B47. Assume that the thickness of the leveling film layer 15 in FIG. 1 is about five times the film thickness of the insulating film 12, and the area of the reflective common electrode B47 or the reflective pixel electrode B45 is about one-tenth of the area of the electrode forming the storage capacitor . Therefore, the size of the small capacitor becomes approximately one-fiftieth of the size of the storage capacitor to be formed. Therefore, when the driving voltage of the offset voltage applied to the reflective pixel electrode and the transmissive pixel electrode is 5V, the voltage of the small capacitor is about 0.1V. This is relatively small compared to the threshold voltage, so it is considered to have no influence on the display.

Fig. 9 shows the equivalent circuit when the small capacitance is not considered. As shown in FIG. 9, the capacitances Cst1 and Cal1 of the reflective region 21 and the capacitances Cst2 and Cal2 of the transmissive region 22 are independent of each other. Therefore, since the reflector 24 is electrically isolated from the reflector 23, even when the potential of the reflector 23 is changed due to the capacitor Cal1, for example, the potential of the transmissive pixel electrode A36 follows the transmissive common signal without being affected by the potential of the capacitor Cal1. Therefore, the potential difference generated between the pixel electrode and the common electrode during the selection period of the scan line 31 can also be maintained during the non-selection period. At the same time, it becomes possible to suppress generation of an offset voltage, and thus light leakage in display of a pixel can be suppressed.

second exemplary embodiment

Next, as the suppression device according to the second exemplary embodiment of the present invention, the capacitance ratio between the storage capacitance using the reflective region and the capacitance formed between the static electrode and the reflector in the reflective region, and the capacitance ratio using the transmissive region will be described. The case of the capacitance ratio between the storage capacitance and the capacitance formed between the static electrode and the reflector in the transmissive region.

Considering that the liquid crystal layer 16 has a property of causing light leakage when an offset voltage exceeding the threshold voltage is applied, the suppressing means according to the second exemplary embodiment of the present invention is constructed so as to utilize the storage capacitance Cst1 of the reflective region 21 The capacitance ratio between the capacitance Cal1 and the capacitance ratio between the storage capacitance Cst2 and the capacitance Cal2 in the transmissive region 22 suppresses the offset voltage to be smaller than the threshold voltage. Hereinafter, a suppressing device according to a second exemplary embodiment of the present invention will be described in a concrete manner.

For the liquid crystal display device according to the second embodiment of the present invention, the same reference numerals are used for the same components as those of the first embodiment described above. In the second embodiment, the system configuration section has almost the same structure as that of the first embodiment. The difference from the first embodiment is that a reflector 25 is provided instead of the electrically isolated reflectors 23 and 24 provided in the first exemplary embodiment.

As in the case of the first exemplary embodiment (FIG. 1) described above, the liquid crystal display device 11 according to the second exemplary embodiment includes a rear side substrate 18 configured with a reflective region 21 and a transmissive region 22, while the reflective common electrode The A37 and the transmissive common electrode A38 are formed on the reflective region 21 side on the observer-side surface of the back-side substrate 18 as shown in FIG. 10 . Also, the scan line 31 (as in the case of FIG. 2 ) is formed on the same plane as the plane on which the reflective common electrode A37 and the transmissive common electrode A38 are formed. As in FIG. 2 of the first embodiment, the transmissive common electrode A38, the scan line 31, and the reflective common electrode A37 are parallel to the direction away from the transmissive region side in the order of the transmissive common electrode A38, the scan line 31, and the reflective common electrode A37. formed. Furthermore, as shown in FIG. 10 , the insulating layer 12 is formed on the viewer side of the back side substrate 18 by covering the transmissive common electrode A38 and the reflective common electrode A37 .

Also, as shown in FIG. 10 , a reflective pixel electrode A35 is formed on the observer side of the reflective region 21 of the insulating layer 12 so as to overlap the reflective common electrode A37 . In other words, the reflective pixel electrode A35 is formed above the reflective common electrode A37 when viewed from the observer side. Thus, the reflective storage capacitor Cst1 is formed on the back side (inside the insulating layer 12 ) of the reflective pixel electrode A35 together with the reflective common electrode A37 . Similarly, a transmissive pixel electrode A36 is formed on the observer side of the reflective region 21 of the insulating layer 12 so as to overlap the transmissive common electrode A38. Thus, the transmissive storage capacitor Cst2 is formed on the rear side (inside the insulating layer 12 ) of the transmissive pixel electrode A36 together with the transmissive common electrode A38 .

Also, just as in FIG. 2 of the first exemplary embodiment, the data line 32 to which the supply data signal is supplied for each pixel is formed, together with the transmissive pixel electrode A38, the scan line 31, and the reflective common electrode A35. Formed perpendicular to each other, the data line 32 is formed on the same plane perpendicular to the plane on which the reflective pixel electrode A35 and the transmissive pixel electrode A36 are formed. As shown in FIG. 2, a switching device (hereinafter referred to as a TFT) for interconnecting each data line 32, the protruding portion of the reflective pixel electrode A35, and the transmissive pixel electrode A36 (the portion encircled by a dotted line) is formed. ). Moreover, as shown in FIG. 10, by covering the observer side of the insulating layer, an insulating layer 13 is formed in the reflective region 21 and the transmissive region 22, and the insulating layer 13 includes a reflective pixel electrode A35 and a transmissive pixel electrode together with the insulating layer. A36.

Also, the organic thin film layer 14 is formed in the reflective region 21 on the observer side of the insulating layer 13 . The organic thin film layer 14 has an uneven pattern on the viewer side surface suitable for a reflector to be described later.

Also, as shown in FIGS. 10 and 11 , a reflector 25 is formed on the viewer side of the organic thin film layer 14 so as to overlap the reflective pixel electrode A35 and the transmissive pixel electrode A36 . That is, the reflector 25 is disposed on the reflective pixel electrode A35 and the transmissive pixel electrode A36 when viewed from the observer side. Thus, capacitors Cal1 and Cal2 are respectively formed between the back side of the reflector 25 and the reflective pixel electrode A35 and the transmissive pixel electrode A36 (the interface between the insulating layer 13 and the organic thin film layer 14 ). Also, the reflector 25 is formed to have an uneven pattern on its cross section to increase the scattering effect.

Further, as shown in FIG. 10 , the leveling film layer 15 is formed by covering the observer side of the reflector 25 of the reflection area 21 and the observer side of the insulating layer 13 of the transmission area 22 with a leveling film. By adjusting the thickness of the leveling film layer 15, the cell gap of each liquid crystal layer in the reflective region 21 and the transmissive region 22 can be adjusted.

And, as shown in FIG. 12 , the comb-shaped reflective common electrode B47 and the comb-shaped reflective pixel electrode B45 are arranged on the viewer side of the leveling film layer 15 in such a way that the protruding parts of the electrodes face the inner side of the reflective region facing in the direction of . Thus, in the reflective region 21 , the reflective pixel electrodes B45 and the reflective common electrodes B47 are arranged in alternating directions in a direction perpendicular to the longitudinal direction of the comb teeth.

Similarly, the comb-shaped transmissive common electrode B48 and the comb-shaped transmissive pixel electrode B46 are arranged on the viewer-side plane of the flattened film layer 15 of the transmissive region 22 in such a manner that the protruding portions of the electrodes face the transmissive region Facing in the direction of the inner side. Thus, in the transmissive region 22, the transmissive pixel electrodes B46 and the transmissive common electrodes B48 are arranged in an alternate manner in a direction orthogonal to the comb tooth longitudinal direction.

As shown in FIG. 12, the reflective common electrode B47, reflective pixel electrode B45, transmissive common electrode B48, and transmissive pixel electrode B46 are respectively connected to the reflective common electrode A37, reflective pixel The electrode A35, the transmissive common electrode A38 and the transmissive pixel electrode A36.

Moreover, as shown in FIG. 10, the liquid crystal display layer 16 is formed on the upper layer (observer side) of the leveling film layer 15 by covering the reflective pixel electrode B45, the reflective common electrode B47, the transmissive pixel electrode B46 and the transmissive common electrode B48. Regarding the liquid crystal layer 16 , its retardation Δnd in the reflective region 21 is set to λ/4, and its retardation Δnd in the transmissive region 22 is set to λ/2. Also, an observer side substrate 19 is provided on the observer side of the liquid crystal layer 16 . Thus, the unit pixel of the liquid crystal display device according to the present exemplary embodiment is configured.

The liquid crystal display device of this exemplary embodiment is constituted as described above, so the reflective common electrode B47 and reflective pixel electrode B45 arranged on the upper layer (observer side) of the leveling film layer 15 and the transmissive common electrode B48 and transmissive An electric field is generated between the pixel electrodes B46 to rotationally drive the liquid crystal.

FIG. 13 shows an equivalent circuit related to a TFT substrate in a unit pixel of the liquid crystal display device 11 shown in FIGS. 10 to 12 . As shown in FIG. 13 , scan lines 31 as control lines for controlling TFTs as switching devices and data lines 32 for supplying pixel electrode voltages to reflective and transmissive pixel electrodes through TFTs are formed to be orthogonal to each other.

With this structure, if the capacitance value formed between the reflective and transmissive common electrodes and between the reflective and transmissive pixel electrodes is C1 (Cst), the capacitors formed between the reflective pixel electrode A35 and the transmissive pixel electrode A36 and the reflector 25 Each capacitance value is C2 (Cal), and α is C2/(C1+C2), the value of α and the potential difference V between the reflective common electrode A37 and the reflector 25 and between the transmissive common electrode A38 and the reflector 25 The relationship of “0.5>V×α” is satisfied.

Also, the capacitance value C3 formed between the reflective pixel electrode and the reflector and the storage capacitance value C4 formed between the reflective pixel electrode and the reflective common electrode satisfy the relationship of "3<C4/C3".

In addition, the capacitance value C5 formed between the transmissive pixel electrode and the reflector and the transmissive storage capacitance value C6 formed between the transmissive pixel electrode and the transmissive common electrode satisfy the relationship of "3<C6/C5".

The storage capacitors Cst1 and Cst2 (hereinafter collectively referred to as Cst) of the reflective region 21 and the transmissive region 22 are connected through capacitors Cal1 and Cal2 (hereinafter collectively referred to as Cal), so there is an offset voltage generated mutually. 14A shows an example of the relationship between the capacitance ratio with respect to Cst and Cal (Cst/Cal) and the offset voltage (ΔV) generated between the transmissive pixel electrode A36 and the transmissive common electrode A38. According to this relationship, as the Cst/Cal value increases, the offset voltage (ΔV) is suppressed.

In addition, FIG. 14B shows an example of a graph regarding the relationship between the transmittance and the applied voltage. Here, the threshold voltage is about 0.7V. For example, "ΔV" indicates a value of 0.7V or less when the ratio (Cst/Cal) between the capacitances (Cst and Cal) is set to 3 or more. This is smaller than the previously set threshold voltage, so light leakage in the transmissive region 22 can be suppressed.

As an example method of increasing the capacitance ratio (Cst/Cal), the film thickness of the organic thin film layer 14 may be increased. Specifically, it is assumed here that there is a pixel structure in which the insulating film layer 12 is made of a SiO film (relative permittivity=4.0) with a film thickness of 0.15 μm and a SiN film (relative permittivity=6.4) with a film thickness of 0.3 μm. ), the insulating film layer 13 is formed with a SiN film with a film thickness of 0.15 μm, and the organic film layer 14 is formed with an acryl-based resin (relative dielectric constant=3.2).

Therefore, when the area of the reflector is twice the area of the electrodes of each of the storage capacitors Cst1 and Cst2 forming the reflective and transmissive regions 21, 22, according to the relationship between the film thickness of the organic thin film layer and the offset voltage shown in FIG. 14C The film thickness of the organic thin film layer for making the offset voltage less than 0.7 V (threshold voltage) is 0.5 μm or more. Thus, even with a structure in which the reflectors are not electrically isolated, the liquid crystal display device of the second exemplary embodiment can suppress the offset voltage and suppress deterioration of visibility caused by light leakage.

third exemplary embodiment

As a third exemplary embodiment, the following will describe a case where a change in wiring is used as the suppressing means of the exemplary embodiment of the present invention.

The suppression device according to the third embodiment has a structure in which the scanning line 31 for supplying the scanning signal to the unit pixel is isolated from the bottom layers of the reflectors 23, 24 and 25, so that the electric field from the scanning line 31 can be arranged to affect outside the region of the potential of reflectors 23, 24 and 25. A third exemplary embodiment of the present invention will be described below. The same reference numerals will be used for the same parts as those of the first and second embodiments described above.

As shown in FIG. 15 , the structure of the unit pixel of the third exemplary embodiment is different from other exemplary embodiments in that the scanning line 31 is provided at the end far from the transmissive region 22 , that is, between the unit pixel itself and At the boundary between the far side pixels leaving the transmissive region 22 . In other words, the scanning line 31 is arranged at a position not overlapping the reflector.

Also, the reflective common electrode A37 is disposed within the reflective region 21 on the same plane as the plane on which the scan line 31 is provided, and the transmissive common electrode A38 is disposed on the transmissive region 22 side apart from the reflective common electrode A37. Thus, TFTs are also formed on the side where the scanning lines 31 are provided. The other structure of this transflective liquid crystal display device is almost the same as that of the second exemplary embodiment described above.

As described above, the electric field generated by the scan line 31 can be suppressed by disposing the scan line 31 on the far side (upper end) from the transmissive region of the unit pixel structure, that is, by providing the scan line at a position not overlapping the reflector. influence on the electric field of the reflector.

In the reflective area of the IPS transflective liquid crystal display device, generally, there is a possibility that the direction of the electric field originally set horizontally to its substrate becomes disturbed due to shift or fluctuation of the potential applied to the reflector.

As described above, by arranging the scan line 31 at the end of the reflective region 21 where the reflector does not overlap the scan line 31 viewed from the observer side, the scan line 31 does not pass through the back side (underlayer side) of the reflector. This makes it possible to alleviate the influence of the electric field generated from the scanning line 31 on the potential of the reflector.

Thus, a potential (electric field) can be applied to the liquid crystal layer of the reflective region 21 in a direction parallel to the substrate. Therefore, the contrast and visibility of the reflection area can be improved.

Fourth Exemplary Embodiment

As a fourth exemplary embodiment of the present invention, a case where part of the storage capacitance Cst2 of the transmissive region 22 is arranged outside the region of the bottom layer of the reflectors 23, 24, and 25 as the suppression means of the embodiment of the present invention will be described below. The same reference numerals are used for the same parts as those of the first, second and third embodiments described above.

As shown in FIG. 16, the unit pixel structure of the transflective liquid crystal display device according to the fourth exemplary embodiment of the present invention has a structure that is disposed not overlapping with the reflectors 23, 24, and 25, that is, between the reflectors 23, 24, and 25. The portion of the storage capacitor of the transmissive region 22 outside the region (specifically, the transmissive portion of the pixel electrode 36 a and the transmissive common electrode 38 a ). As shown in FIG. 16, in this exemplary embodiment, portions of the transmissive common electrode 38a and the transmissive pixel electrode 36a are arranged on the far side away from the reflective region 21 side (the portion with oblique lines shown in FIG. 16). At the ends within the transmissive region 22 . Thus, part of the storage capacitance of the transmissive region 22 is formed between the transmissive common electrode A38 and the transmissive pixel electrode A36 illustrated with oblique lines.

As described above, the storage capacitors of the reflective region 21 and the transmissive region 22 of the first to third exemplary embodiments are provided at positions where the bottom layer of the reflector overlaps the reflector. However, the fourth exemplary embodiment is different from the other embodiments in that part of the storage capacitance of the transmissive region 22 is provided at a position not overlapping the reflector.

In this case, a structure for preventing reverse rotation of liquid crystal molecules can be provided to the transmissive common electrode and the transmissive pixel electrode disposed at positions on the bottom layer of the reflector that do not overlap the reflector. This particularly makes it possible to suppress disclination at the upper and lower ends of the transmissive region, and thus the visibility of the liquid crystal display device can be improved.

Although the first to fourth embodiments have been described above with reference to the case of the IPS transflective liquid crystal display device, the present invention is not limited to this case. The present invention can also be applied to TN, VA, and FFS transflective liquid crystal display devices.

Next, another exemplary embodiment of the present invention will be described. A transflective liquid crystal display device according to another embodiment of the present invention has a back side substrate, an observer side substrate, and a liquid crystal layer interposed between the two substrates, and is provided with unit pixels (each including a A reflective area for reflected light from the observer side and a transmissive area for transmitted light from the rear side). The transflective liquid crystal display layer may be formed in a structure in which: a pair of electrically isolated reflectors 1 and 2 are formed in the reflective area; reflective pixel electrodes for the reflective area and the transmissive area each driven by a data signal and a transmissive pixel electrode, or a reflective common electrode and a transmissive common electrode driven by a common signal, are provided on the back side substrate side of the reflectors 1 and 2; and between the reflective pixel electrode and the transmissive pixel electrode and between the reflective common electrode and A storage capacitor is formed between the transmissive common electrodes.

Also, unit pixels (each including a reflective region for reflecting reflected light from the observer side) having a back side substrate, an observer side substrate, and a liquid crystal layer sandwiched between the two substrates and configured to drive the liquid crystal layer are provided. and the transflective liquid crystal display device for transmitting the transmitted light from the back side) can be formed in this structure, wherein: the reflective pixel electrode and the transmissive pixel electrode each driven by a data signal are in the reflector The reflective region and the transmissive region are provided on the backside substrate side; reflective common electrodes and transmissive common electrodes are provided on the backside substrates of the reflective pixel electrodes and the transmissive pixel electrodes, respectively, for forming storage capacitors with the reflective pixel electrodes and the transmissive pixel electrodes and, if the capacitance value formed between the reflective and transmissive common electrodes and the reflective and transmissive pixel electrodes is C1, the capacitance formed between the reflective and transmissive pixel electrodes and the reflector is C2, and α is C2/(C1+C2 ), the value of α and the potential difference V between the reflective and transmissive common electrodes and the reflector satisfy the relationship of “0.5>V×α”.

Also, the transflective liquid crystal display device may be constructed in such a manner that the capacitance value C3 formed between the reflective pixel electrode and the reflector and the reflective storage capacitance value C4 formed between the reflective pixel electrode and the reflective common electrode satisfy "3 <C4/C3", and the capacitance C5 formed between the transmissive pixel electrode and the reflector and the transmissive storage capacitance C6 formed between the transmissive pixel electrode and the transmissive common electrode satisfy the requirement of "3<C6/C5" relation.

Thereby, the aperture ratio can be increased in the liquid crystal display in the reflective region and the transmissive region. At the same time, it is possible to effectively suppress light leakage of the liquid crystal portion, and improve contrast and visibility.

Also, a scan line for supplying a scan signal to each unit pixel may be arranged at an end of the reflective area within the unit pixel on the side away from the transmissive area.

This makes it possible to suppress the influence of the potential applied to the reflector by the scanning line, thus enabling improvement of contrast and visibility in the reflective area.

Also, a partially transmissive pixel electrode and a transmissive common electrode may be provided at an end of the transmissive region that does not overlap the reflector.

Visibility of the transmission area can be improved by providing a structure for suppressing disclination generated in upper and lower portions of the transmission area when the liquid crystal display is driven.

Also, as a mode for driving the liquid crystal layer of each unit pixel, any one selected from IPS (In-Plane Switching), FFS (Fringe Field Switching), VA (Vertical Alignment), and TN (Twisted Nematic) can be used. mode.

While the invention has been particularly shown and described with reference to exemplary embodiments thereof, the invention is not limited to these embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the claims.

Industrial applicability

The present invention is preferably applicable to liquid crystal display devices of portable terminal devices such as cellular phones, game machines, digital cameras, and video cameras.

Claims (9)

1. transflective liquid crystal display device comprises: in unit picture element, have the reflector space of reverberator and paired pixel electrode and public electrode and have paired pixel electrode and the regional transmission of public electrode; And the liquid crystal layer that offers said reflector space and said regional transmission, said transflective liquid crystal display device also comprises:

Be provided at the MM CAP that is used for said reflector space and said regional transmission between said pixel electrode and the said public electrode; In the layer of said MM CAP below the said reverberator of said reflector space, the current potential that said MM CAP is respectively applied for through the said public electrode in current potential of following the said public electrode in the said reflector space and the said regional transmission changes the current potential of the said pixel electrode in the said reflector space and the current potential of the said pixel electrode in the said regional transmission; And

Restraining device; The light that is created in the said liquid crystal layer when being used for suppressing the influencing of current potential that static electrode when the static electrode of the said MM CAP of said reflector space and the said MM CAP in the said regional transmission receives said reverberator leaks, and this influence is owing to the capacitive coupling that produces between capacitive coupling that produces between the said static electrode in said reverberator and said reflector space and the said static electrode in said reverberator and said regional transmission causes.

2. transflective liquid crystal display device as claimed in claim 1, wherein

Said restraining device comprises: as first reverberator and second reverberator of said reverberator, said first reverberator and said second reverberator be physical separation each other, and

Said restraining device has following structure: the static electrode and the electric capacity between said second reverberator that in this structure, are formed on the static electrode and the electric capacity between said first reverberator of said reflector space and are formed on said regional transmission are that electricity is isolated.

3. transflective liquid crystal display device as claimed in claim 1, wherein:

Said liquid crystal layer has such characteristic, promptly when the offset voltage that applies above threshold value, produces light at said regional transmission and leaks; And

Said restraining device is configured to through the said MM CAP of utilizing said reflector space and is formed on the said static electrode of said reflector space and the capacity ratio between the said electric capacity between the said reverberator; And the said MM CAP of said regional transmission and be formed on the said static electrode of said regional transmission and the capacity ratio between the said electric capacity between the said reverberator, suppress said offset voltage with less than said threshold value.

4. transflective liquid crystal display device as claimed in claim 3, wherein:

If the value of the said MM CAP in said reflector space or said regional transmission is C1; Being formed on the said static electrode of said reflector space or said regional transmission and the value of the said MM CAP between the said reverberator is C2; And α is C2/ (C1+C2), the value of α and said reverberator and and the paired reflection public electrode of the said static electrode of said reflector space or said regional transmission between potential difference (PD) V satisfy the relation of " 0.5＞V * α ".

5. transflective liquid crystal display device as claimed in claim 3, wherein:

The storage capacitance value C4 that is formed on said static electrode and the capacitance C3 between the said reverberator and the said reflector space of said reflector space satisfies the relation of " 3＜C4/C3 ".

6. transflective liquid crystal display device as claimed in claim 3, wherein:

The storage capacitance value C6 that is formed on said static electrode and the capacitance C5 between the said reverberator and the said regional transmission of said regional transmission satisfies the relation of " 3＜C6/C5 ".

7. transflective liquid crystal display device as claimed in claim 1; Wherein be used for supplying with the bottom isolation of sweep trace with the said reverberator of sweep signal, beyond the zone that is disposed in from the current potential of the said reverberator of influence of said sweep trace to said unit picture element.

8. transflective liquid crystal display device as claimed in claim 1, the said MM CAP of the part of wherein said regional transmission are disposed in beyond the zone of bottom of said reverberator.

9. transflective liquid crystal display device as claimed in claim 1, it is driven by the transverse electric place that is created between said pixel electrode and the said public electrode.

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